U.S. Pat. No. 1,542,016 to Stull, incorporated herein in its entirety by this reference, discloses a "permutation" lock with an essentially symmetric, "substantially C-shaped" shackle. Also included as part of the permutation lock are a sleeve surrounded by an "operating barrel," manipulation of which will move the sleeve. Properly turning the barrel, therefore, allows both it and the sleeve to "be bodily moved back upon the shackle" and open the locking mechanism.
U.S. Pat. No. 5,433,092 to Kuo likewise discloses a keyed lock with a symmetric shackling system. Formed of two rods (rather than the one of the device of the Stull patent), the lock of the Kuo patent contemplates connecting the rods with a pin or bolt remote from the housing containing the locking mechanism. Normal use of the lock almost certainly requires two hands, one to use the key to manipulate the mechanism and the other to grasp and move at least one of the two rods.